Analysis And Treatment On The Assembly Homogeneous Few-group Cross-sections

In the current generation of core physics calculations, assembly homogenizationtechnique is one of the major source of error. Thermal parameters and depletion have asignificant effect to the cross section, mainly reflecting the changes of the neutron energyspectrum and the nuclei, and then lead to changes in the assembly cross section. In order toobtain accurate power distribution, effective cross section expression is necessary.In this study, the cross section of the assembly with the burnable poison in the QinshanNuclear Power Station is studied, taking into account depletion, boron concentration, fueltemperature，moderator temperature，shutdown cooling time and history effect on the crosssection. CASMO4E is used to calculate the cross section under various operating condition.Further more polynomial fitting algorithm, stepwise regression algorithm and interpolationalgorithm are used for function approximation of the cross section.Sample cross section is stored in a certain table form in the interpolationalgorithm.Cubic spline interpolation is implemented to obtain the appropriate assemblycross section. Finally we build a relation database using these tables based on vc6.0and mysql.The cross section is expressed as the number of sub-section in polynomial fittingalgorithm, for each sub-section was fitted by polynomial. FITLINK procedure is used onthe sample cross section of polynomial fitting, using programs written in MATLABlanguage to read the output coefficients which construct fitting formula.Stepwise regressioncan select the different significant effect factors on the different cross sections. And themajority of the fitting formulas are with the physical meaning. In the premise of ensuringthe accuracy, the fitting formulas of low sub-item construct are selected.Using these methods, we can solve the neutron diffusion equation using the obtainedcross sections and the results show that these methods are feasible.